Sulphonic acids of aromatic diisocyanates or polyisocyanates are known (see, e.g., German Offenlegungsschriften Nos. 2,227,111 and 2,359,615 and U.S. Pat. No. 3,826,769). They may be readily obtained by reacting the corresponding aromatic diisocyanates or polyisocyanates with sulphonating agents, such as sulphur trioxide, adducts of sulphur trioxide, oleum, chlorosulphonic acid or sulphuric acid. The products obtained may be solid, resinous or pulverulent sulphonation products, or solutions or dispersions of the sulphonated isocyanates in unreacted starting material, depending on the isocyanate used and the degree of sulphonation and nature of the sulphonating agent.
The preparation of polyurethanes or polyurethane ureas from polyisocyanates containing sulphonic acid groups has been described, for example, in U.S. Pat. No. 3,826,769 and in German Offenlegungsschrift No. 2,359,611. Polyurethanes and polyureas which have been modified with sulphonic acid or sulphonate groups in this way are frequently very hydrophilic. For this reason, the sulphonic acid group content is generally kept as low as possible. Partially sulphonated polyisocyanates or solutions of isocyanato sulphonic acids in polyisocyanates are therefore of particular importance. The major advantage of sulphonated polyisocyanates relates to the high polarity of sulphonic acid groups. This high polarity results in marked interaction or adhesion in polar media, such as water, or with moist polar substrates, and particularly those of an inorganic nature.
On the other hand, chemically pure and especially sulphonated isocyanato sulphonic acids have high melting points, low solubility in organic media and extreme sensitivity to water and atmospheric moisture. These properties render the products difficult to process. The acid character thereof is also frequently a disadvantage. Discoloration and premature degradation of polyurethanes prepared from these compounds make the products difficult to use in practice. Although these phenomena may be prevented by suitable methods of neutralization, the hydrophilic character of the products is thereby increased.
There is therefore a demand for polyisocyanates which would combine the polar character and its attendant advantages, such as low vapor pressure and improved bonding properties, with a predominantly hydrophobic character. There is also a demand for readily accessible aromatic polyisocyanates which would give rise to toxicologically harmless products when the oligomers and polymers produced from them are degraded by hydrolysis.